In recent years, as digital cameras have been in widespread use, there are growing demands for small-size lenses. As an optical glass material for producing such small-size lenses, a high-refractivity glass having a refractive index (nd) of over 1.8 is suitable.
However, in conventional glasses, disadvantageously, the coloring tendency thereof is intensified, or the stability of glass production is decreased, with an increase in the refractive index. In particular, when the coloring tendency is intensified, a digital camera or the like has a problem that since CCD and the like are used in an image sensing device, the sensitivity to blue on a short wavelength side among three primary colors is decreased when an imaging system is seen as a whole.
Further, as a high-refractivity glass having a refractive index (nd) of over 1.8, there are known glasses that are used as ophthalmic lens materials such as glasses disclosed in JP-A-3-5340, JP-A-6-56462 and JP-A-6-87628, although they are not used for a camera lens. While these glasses have low densities and are excellent as ophthalmic lens materials, they are not suitable from the viewpoint of an improvement in production stability due to a high priority put on a decrease in density.